1. Field of the Invention
The present invention broadly relates to a dielectric resonator device, and, more particularly, to a structure of a dielectric resonator device which allows an external coupling of a dielectric resonator to be performed readily, and excellent workability and processability to be achieved.
2. Description of the Related Art
FIG. 4 is a side elevational view which schematically shows a structure of an external coupling of a dielectric resonator.
As illustrated in FIG. 4, in the structure, a coupling loop 59, composed of a metallic wire connected to an external connector 58, is externally coupled to a dielectric column 60. More specifically, when an electrical current E is allowed to flow in the coupling loop 59 in the direction of the arrows, a magnetic field M is generated around an axis defined by the coupling loop 59. The generated magnetic field M causes the coupling loop 59 and the dielectric column to be coupled together. Here, the degree of coupling of the coupling loop 59 and the dielectric column 60 depends on such factors as the thickness of the metallic wire making up the coupling loop 59, the size of the coupling loop 59, the distance between the coupling loop 59 and the dielectric column 60, and the like.
FIGS. 5(A) and 5(B) each illustrate an example of a dielectric resonator device using the dielectric resonator shown in FIG. 4.
FIG. 5(A) is a plan view of the internal construction of the dielectric resonator device, without the upper portion of the case. FIG. 5(B) is a side elevational view thereof.
As shown in FIGS. 5(A) and 5(B), six dielectric resonators, R1 to R6, are contained in a case 30. The first three dielectric resonators R1 to R3 form a receiving bandpass filter, while the last three dielectric resonators R4 to R6 form a transmitting bandpass filter. External connectors 31 to 33 are provided on the side faces of the case 30. Coupling loops 34 and 35 are provided between the central conductor of the external connector 32 and the case 30, and between the central conductor of the external connector 33 and the case 30, respectively. The case 30 serves as a ground. The coupling loops 34 and 35 are magnetically coupled to the dielectric resonators R1 and R4, respectively.
FIG. 3 is a partial perspective view of the structure of the region around the external connector 31. As illustrated in FIG. 3, a central conductor 31a of the external connector 31 is connected to the coupling loop 21.
The coupling loop 21 is formed by a main wire 22 and four branch wires 23. The main coupling of the coupling loop 21 to the dielectric resonators R3 and R6 is performed through the four branch wires 23.
The main wire 22 is provided with two phase adjustors 24. The central conductor portion 31a of the external connector 31 is soldered at 26 to the center of the main wire 22. Each end of the main wire 22 is connected and fixed to the case 30, serving as ground, via terminals such as solderless terminals 27 or the like which are then screwed to a grounded mounting post.
When the coupling loop 21 is magnetically coupled to the dielectric resonators R3 and R6, the two phase adjustors 24 adjust the phase of the dielectric resonator R3 and the central conductor 31a, and the phase of the dielectric resonator R6 and the central conductor 31a, respectively. The two phase adjustors 24 adjust an electrical length from the central conductor 31a to the dielectric resonator R3 and an electrical length from the central conductor 31a to the dielectric resonator R6, whereby the two phase adjustors 24 adjust the phase of the transmitter and the phase of the receiver. The phase adjustors 24 are thought to adjust the phase of the dielectric resonator R3 and the central conductor 31a, and that of the dielectric resonator R6 and the central conductor 31a, respectively, when the equivalent inductive components of the phase adjustors 24 are introduced in parallel with the four branch wires 23 which are used for the main coupling of the coupling loop 21 with the resonators R3 and R6, and the branch wires 23 and the dielectric resonators R3 and R6 are coupled together.
The center of the main wire 22 is supported by two cylindrical bushings 28 made of fluororesin.
The four branch wires 23 are C-shaped. A projecting end of each of the C-shaped branch wires 23 is inserted in a hole formed in the main wire 22 and soldered thereto, while the other end of each branch wire 23, provided with one of the solderless terminals 27, is connected and fixed to the case 30, serving as ground, along with the ends of the main wire 22.
The coupling of the coupling loop 21 with the dielectric resonators R3 and R6 is adjusted using an adjusting jig, with the upper portion of the case 30 removed, or through a hole for receiving the adjusting jig into the case 30. Here, the adjustment is performed using the adjusting jig by bending the branch wire 23 of the coupling loop 21 such that the loop 21 approaches the case 30 (that is, moves away from the dielectric resonators R3 and R6), or by bending the branch wire 23 such that the loop 21 approaches the dielectric resonators R3 and R6 (that is, moves away from the case 30). In other words, the adjustment is performed by moving the branch wires 23.
Conventional coupling loops are formed by metallic wires, with a hole formed in a main wire of the coupling loop for inserting an end of a branch wire therethrough and soldering the branch wire thereto. However, it is extremely difficult to form such a hole in a thin metallic wire, making it very troublesome to produce the coupling loop.
Even when the coupling loops are constructed such that they can be externally coupled to a desired degree, the coupling loops vary slightly in form after they are constructed, and variations occur in the degree of external coupling of the dielectric resonator devices, thus requiring large adjustments of the coupling loops.
In addition, many component parts are used, including a main wire having a portion for coupling to the central conductor of the external connector and having two phase adjustors, four branch wires, a bushing for supporting the main wire, and a solderless terminal for being screwed to a ground.
Further, since the coupling loop is formed by a metallic wire, the metallic wire must be shaped into a desired form after it has been formed to a proper length, thus making it very troublesome to produce the coupling loop.
This has made it more expensive to produce a dielectric resonator device.
Further, since an adjusting jig is used to adjust the degree of external coupling by moving the branch wire, a load is exerted on a soldered connecting portion of the coupling loop, resulting in peeling of the solder or removal of the end of the inserted metallic wire, so that the characteristics of the coupling loop are changed from their predetermined value, leading to the possibility of deviations in the characteristics of the entire dielectric resonator device from the desired characteristics.